Bugs, bees and birds bring beneficial biodiversity

Lately we have been hearing a lot more about biodiversity in the garden and in particular the diversity of insect life that can and should exist in a healthy garden. As we rush through our gardens on the way to work or school we barely notice insects. If we slow down a little we may notice the odd bee or butterfly or grasshopper, and as we take the time to stop and sit in the garden and really watch what is happening we soon start to notice a variety of different bees, wasps, flies, dragonflies, beetles and bugs.

This blue sage (Eranthemum pulchellum) is covered in mealy bug but is huge and flowering very happily – not at all bothered by the mealy bugs. After flowering I will cut it back hard which will remove the pests, and let the chooks clean up the branches before turning them into cutting pieces.

I encourage you to seek out further information about the insects of your region, to notice what is living in your garden and see how over time as you grow more flowers, you will see a greater variety of insects. More and more good resources are becoming available these days as information about good bugs becomes more sought after but there are still many insects that are barely known or not known at all. This is because they are; let’s face it, small and not the most obvious things in the garden.

A number of websites such as Wild Pollinator Count and Bowerbird encourage you to record what you find and enter this information into their databases. The app “Organic Gardening and Insects” by Biological is a very helpful resource, especially to have with you whilst gardening, and a good website to look up what you find is Brisbane Insects. Entomology Resources will lead you to other sites in Australia and overseas.

The yellow ladybirds eat powdery mildew

These sorts of programs are not only informative for us, but help researchers gather information about the distribution of different species and even find new species. Gardeners are playing a very important role in furthering scientific knowledge of insects, even gardeners in busy urban areas are finding new species of insects – and you thought the only species left to discover where in remote wilderness!

All of this is actually extremely important to us as gardeners. Why? Because one of the key activities we all engage in is pest control. This is also one of the least environmentally friendly of the gardening tasks. Most of us have a shelf full of various poisons to help with the task. Even organic gardeners will find they have a variety of homemade or organic sprays with which they are armed and ready for garden warfare. In fact, there are many books dedicated entirely too organic remedies for various pests and diseases – entire books on how to kill bugs ‘organically’.

The yellow hairy flower wasp is known to parasitise scarab beetle larvae – those curl grubs which we hate finding in pots and in the lawn.

Even the organic sprays are killers. Sure they are infinitely better than a lot of commercially available chemicals (which have been shown to have environmental impacts beyond killing the bugs they were originally intended for), but they are still general killers of whatever they come into contact with during their much shorter active life. Pyrethrum and nicotine sprays are examples. They are both derived from plants, and therefore organic, but they are also very good at killing insects of all persuasions.

Pyrethroid and neonicotinoid sprays are synthetic chemicals based on their natural counterparts, but with the added deadly effect that they are more UV stable and therefore persist in the environment longer. This is great news for farmers in that they can spray pests less often, but not great news for insects.

The robber fly here is eating a bee. they catch and eat flying insects which sometimes includes bees but also included flies and grasshoppers

Homemade white oil sprays are great, but they do contain detergents and vegetable oils which are highly processed products, and they do suffocate all insects that they are sprayed on.

To be a truly sustainable gardener, I encourage you to throw away almost all of your sprays. I do have a homemade white oil spray, and a pyrethrum spray in my gardening arsenal, but they very rarely come out. Instead I focus on healthy soil, so that my plants are healthy enough to fight off the odd bug or two. I grow a diverse garden with lots of different flowers and plant types, with the intent of providing food and habitat for a wide variety of bugs – good and bad, thereby inviting them to make my garden their home.

Grasshopper affected leaves of the angels trumpet – a few holes in the leaves won’t upset the plant and needn’t upset the gardener either

By allowing the good bugs to set up camp in your garden, they will do almost all of the pest control for you. I love that this saves me time and money on sprays. It also saves the bees and butterflies and even up the food chain to birds and lizards from being wiped out by our poisons. In order for this to happen, we do need to leave alone some of the bad bugs too. It may seem counterproductive but the plant pests are food for the beneficial insects we are trying to attract, so we need to allow some of their food to remain in order for the beneficial insects to have something to come for. A constant small supply of food means that there is a constant supply of good bugs feeding on them, and the system remains in healthy balance. If the bad guys are entirely wiped out, the good guys have no food, and will not be there when we want them to be.

Leaf cutter bees love roses – these holes in the leaf were made by leaf cutter bees, not caterpillars. Notice the holes are all the same shape – either circular or ovoid

Be patient. You may need to hand squash an infestation that seems to be getting too much, but try not to spray, as the good guys are on their way. I know it’s hard – I was getting very fed up with aphids on a client’s roses. I had hand squashed them all twice and still they were back in their thousands on my next visit. As I pulled out the pyrethrum and started spraying, I noticed the ladybugs. Finally! I stopped spraying immediately and by the next visit, there were only a few aphids and the roses were flowering like mad. Balance had been restored. An adult lady bug can eat up to 50 aphids a day; the larvae (which look nothing at all like the adults) can eat even more.

The metallic ladybirds eat aphids and scale

Gardening personality Jerry Coleby-Williams has identified almost 400 different insect species in his Brisbane suburban garden. I have no idea how many different insects I have, but I do like to sit in the garden with a cuppa and observe the variety – me knowing what they all are has no bearing on them getting on with creating a healthy and diverse ecosystem in my garden. My role is to facilitate and appreciate their presence.

Mind you, finding out more can be fun. I left the windows in my car open one night and when driving the next day, my son and I noticed a very attractive small black flying thing with a shiny silver abdomen. It turned out to be an anthrax bee fly which had a nesting hole in the timber fence, and which feed on ant lions. So we hunted around and happily found some ant lion nests, grateful that there was something eating our plague of ants!

Green lacewings eggs on a succulent

On further investigation we found that ant lions are the larvae of the green lacewing, which we often see indoors although they eat aphids and scale, and that what we had thought were spider eggs on a leaf were actually lacewing eggs. The most wonderful aspect of all of this is just how interconnected all these different insects are. Just like a country town where everyone knows each other, if something bad happens to someone, the impacts are far reaching within the community, so it is with our garden insects. The opposite is also true – as community support keeps a country town going, so to do these insects work together in ways far more complex than we know, to keep our gardens healthy.

As I look out of my office window I can see a mealy bug infestation at the top of my Rose of Sharon. It is only on a couple of branches, most are fine, and it is out of reach so I will leave it for whoever comes along to eat them. The tree is getting on a bit and they are short lived so this reminds me that it might be time to let a seedling or two come up and remain so that they can take over the place of the parent tree in a year or two. All the sprays in the world will not make this small tree live forever. A bit of extra compost and a good watering will get the best out of the last couple of years I have in this tree. As it senesces it will be attacked more by bugs, which will in turn feed more good bugs. The branches and trunk will become softer, with hollow spots which will become nesting spots for lots of solitary bees and other good bugs and the leaf drop will add organic matter to the soil. And it has not given up the ghost yet – it is still an attractive small tree that flowers beautifully and provides welcome shelter for the garden below.

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About Kate Wall

Kate has gardened since she was a child. Gardening as a profession came almost by accident - after volunteering to rescue flooded gardens and working in over 100 gardens, she felt her trial by flood had directed her to her true calling, and she has gardened professionally ever since. Kate is primary care giver to approximately 20 gardens concurrently (including her own), in addition to consulting, garden makeovers and creating new gardens. She lives and works in Brisbane, Queensland, and is passionate about gardening to suit our sub-tropical climate.